The present invention relates generally to semiconductor circuit designs, and more particularly to integrated circuits with a high operation speed and low power consumption.
As integrated circuit designs become more complicated, their power consumption has become a major design concern. Most of today's integrated circuits incorporate some sorts of power saving techniques for reasons, such as cost efficiency. Power saving techniques include, for example, disabling peripheral devices, standby mode designs and many other methods. High power consumption exacerbates reliability problems by raising the operating temperature of an integrated circuit. It also intensifies the current flow in a power supply line, thereby causing electro-migration problems. In addition, since the power dissipated by an integrated circuit is directly proportional to the square of the power supply voltage, high power consumption exponentially impacts battery-powered portable devices by requiring either a large battery pack or an unacceptably short operating time.
As such, there have been many efforts to reduce the power consumption of an integrated circuit. For example, the power supply voltage can be reduced from a higher voltage level, such as 5V, to a lower voltage level, such as 3.3V and below. As another example, an integrated circuit can be implemented with a standby scheme, which cuts off the power supply to certain circuit modules in the integrated circuit when it idles for a predetermined period of time.
While the standby scheme is useful in reducing the power consumption of an integrated circuit, it certainly can be further improved. For example, a leakage current still occurs, when the power supply is not fully cut off to the circuit modules. Various conventional methods are used to avoid such current leakage. One method is to use devices of multiple threshold voltages. The high threshold voltage devices are used as switches between power supplies and circuit modules, since they can be more fully turned off than the low threshold voltage devices. This helps to reduce the leakage current from the power supplies to the circuit modules.
There are many ways to implement the multiple threshold voltage devices by, for example, varying the gate oxide thickness, doping densities or channel lengths. However, this requires separate sets of masks and process steps to form the devices of various threshold voltages. As a result, it incurs additional fabrication costs. It is possible to realize multiple threshold voltages for devices of the same physical dimensions and properties by modulating the biases applied to their bodies. However, these devices have a slower operation speed, due to the time needed to charge their bodies and wells.
What is needed is an integrated circuit with a low power consumption and high operation speed.